The present invention relates to an exposure device for use in a copying machine, an optical printer, or other image recording apparatus.
Japanese Laid-Open Patent Application Kokai Nos. 58-23025 and 58-88739 disclose a photosensitive sheet suitable for use as a copying sheet which is coated with microcapsules encapsulating chromogenic material (dye precursors), photo-curable resin, a photosensitizer, and a photopolymerization initiator, and also with a color developer which will react with the dye precursors to develop colors. The encapsulated materials and the developer material are co-deposited on one surface of a single substrate as one layer or as two contiguous layers. Such type of image recording medium is generally referred to as self-contained type recording medium as typically disclosed in U.S. Pat. No. 4,440,846.
When light is applied to the coated layer on the photosensitive sheet, those microcapsules which are exposed to light are photo-cured, and those which are not remain unset. Therefore, by subsequently pressing the photosensitive sheet between pressing rollers, the unset microcapsules are ruptured to allow the dye precursors to react with the color developer for producing a desired copy image. Where the photo-sensitive sheet is used as a copying sheet, a copy bearing a high-quality image reproduced with good resolution and sharpness can be produced. Since no toner is employed, unlike copying machines using plain paper, the copying machine which utilizes photosensitive sheets requires easy maintenance.
The photosensitive sheet described above is of the self-contained type. However, a transfer-type photosensitive sheet has also been developed. The transfer-type photo-sensitive sheet is coated with only microcapsules, but not a color developer, and is used in combination with a transfer sheet that is coated with a color developer. After the photosensitive sheet has been exposed to light, the transfer sheet is placed over the photosensitive sheet, and they are placed under pressure to develop an image on the transfer sheet. The transfer-type photosensitive sheet also offers the same advantages as those of the self-coloring photo-sensitive sheet. The transfer type image recording medium is best disclosed in U.S. Pat. No. 4,399,209 in which the developer material is coated on a separate substrate as a separate developer or copy sheet.
A photosensitive sheet, whether it may be of the self-contained type or the transfer-type, is usually held flatwise by being placed on a flat sheet holder or tensioned between two rolls in order to avoid defocusing or image distortion while the photosensitive sheet is being exposed to light. If light emitted from a light source and passed through the photosensitive sheet is reflected by the surface of the sheet holder, the photosensitive sheet is exposed again to the reflected light. When such double exposure is caused, the profile of the image produced by the light coming from the light source tends to be blurred by the subsequent reflected light, resulting in a lower degree of resolution.
The sensitivities at respective wavelengths of photosensitive sheets vary from lot to lot when they are manufactured. Any such varying sensitivities appreciably affect the color-tone or balance and reproducibility of developed colors. To avoid this problem, when an image is to be reproduced in a copying machine using a photosensitive sheet, the data on reference sensitivity levels indicated on the sheet package must be provisionally inputted by an operator into the copying machine. This data input procedure makes the copying process less efficient. Further, the cost of the copying machine must be increased since it must have a data input unit and a color correcting unit.
Commonly assigned co-pending U.S. patent application Ser. No. 089,608 filed Aug. 25,1987 discloses an exposing apparatus which includes a sheet mount for mounting the photosensitive pressure sensitive sheet thereon for exposing the same to light, and a surface-finished reflectivity means provided on a mounting surface of the sheet mount so as to eliminate diffused reflection and to avoid defficiencies attendant to the above-described double exposure.
Further, commonly assigned co-pending U.S. patent application Ser. No. 154,235 filed Feb. 10, 1988 discloses a color-tone controlling method and apparatus at an exposure zone. The latter invention employs a plurality of color-tone controlling plates selectively positioned underneath the photosensitive medium. When an upper surface of the photosensitive recording medium is subjected to irradiation with light which carries one of the color images, the light passing through the sensitive sheet is reflected at the selected color-tone plate whose color is identical with that of the color image, so that the light is again entered into the photosensitive sheet from its lower surface, to thereby attain double exposure for conpensating the color-tone of the resultant color image on the photosensitive sheet. If the photosensitive sheet does not provide its ideal photo-sensitivities, an operator selects one of the color-tone controlling plates for the double exposure so as to obtain color in the final output image.